Frameworker247 - 1 year ago 52

R Question

I'm sure there is a super-simple solution to this, I just can't figure out what it is.

I have a long, single-variable dataset in R. I can identify the beginning and end of the multiple relevant ranges throughout, I just need to filter out the rest.

So given a vector x:

`> x <- c(2400:2600)`

And vectors of start points and end points:

`> startpoints <- c(1,11,101)`

> endpoints <- c(3,13,103)

I need to return the subset of x that looks like this:

`> x[c(1:3, 11:13, 101:103)]`

[1] 2400 2401 2402 2410 2411 2412 2500 2501 2502

I've tried this:

`> x[startpoints:endpoints]`

But R just takes the first value from each vector and returns that series:

`[1] 2400 2401 2402`

...with a couple of warnings

My startpoints and endpoints vectors should always be equal in length, although they may vary together in length with different datasets.

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Answer Source

We can use `mapply`

to get the sequence between corresponding elements of 'startpoints', 'endpoints' and this can subset the 'x' vector.

```
x[mapply(`:`, startpoints, endpoints)]
#[1] 2400 2401 2402 2410 2411 2412 2500 2501 2502
```

If the sequence are of different lengths, as @nicola mentioned, `mapply`

returns a `list`

, so we need to `unlist`

it

```
x[unlist(mapply(`:`, startpoints, endpoints))]
```

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